Internal fuel tanks are standard components of craft powered by combustion engines. A refueling point is consequently required through which the internal fuel tank can be refilled. Commonly the refueling point consists of an aperture which can be closed by a cap.
A potential problem with refueling via an external aperture occurs when the tank becomes full. Because the level of fuel in the tank cannot be visually monitored, additional fuel may be inadvertently added, which backs up and then overflows from the refueling aperture. Because the rate of such overflow will be equivalent to the rate at which fuel is being pumped, a considerable amount of overflowing fuel may accumulate very quickly.
One solution to this problem is to position sensors in the fuel pump to cut the flow when the tank is full. However it is not always appropriate to supply fuel to some types of vehicle, for example marine craft, using this type of fuel pump.
The problem of fuel overflow is particularly acute when the position of the refueling aperture is such that any overflow accumulates within a vehicle, rather than draining away outside the vehicle. This is a particular problem in boats and ships and most particularly in inflatable marine craft where there is a limited choice of positions for the refueling aperture.
The inboard accumulation of fuel represents a major safety hazard and overflow from refueling can be a significant cause of such an accumulation.